To date, study of the microcirculation has been limited almost exclusively to stationary tissue. Thus, the microvasculature of the myocardium has not been studied extensively using intravital microscopy techniques because of the inherent myocardial motion. Presently, little is known at the microvascular level in the heart about pressure distribution, pressure fluctuations, diameter fluctuation and functional significance of the collaterals. The object of this proposal is to develop a technique which uses a synchronized strobe light and a computer controlled electromechanical micromanipulator designed to follow cardiac motion, thereby allowing pressure and diameter measurements in the beating in situ heart. These techniques will then be used to examine myocardial microcirculation pressures and diameters in order to develop the basic foundation necessary to understand the functional characteristics of the myocardial microvasculature. Particular attention will be given to pulsatile characteristics in order to understand vascular compression unique to the working heart. This will involve frequency analysis to examine harmonic amplitude and phase angles for a broad range of arterioles and venules. Using ophthalmic cautery technique, ischemic myocardium will be examined so that the effect of myocardial compression on vascular volume can be studied and the significance of collateral circulation evaluated. This basic foundation will provide needed information concerning the site and size of resistance vessels, the location and significance of vascular compression in terms of resistance changes and volume shifts and the significance and function of the coronary collateral circulation. It develops a foundation on which other investigations (e.g., drug interventions) can be based and provides direction for the treatment of ischemic heart disease.